Solid-State Preparation and Electrochemical Properties of Mg2+-Doped Life0.7mn0.3po4/C

Abstract

A series of LiFe 0.7 Mn 0.3-x Mg x PO 4 /C (x=0, 0.02, 0.05 and 0.08) cathode materials were synthesized by high temperature solid phase method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical tests for structural, morphological and electrochemical properties of the synthesized materials. The experimental results show that the small amount of Mg 2+ doping not only has no effect on the crystalline structure of the material, but also significantly improves the electrochemical properties of the material. The LiFe 0.7 Mn 0.25 Mg 0.05 PO 4 /C material achieves a specific discharge capacity of 163.2, 155.2, 149.1 and 142.0 mAh/g at 0.1 C, 0.2 C, 0.5 C and 1 C, respectively, and a capacity retention rate of 98.6% after 50 cycles at 0.1 C. It exhibits excellent rate performance and cycle stability. Electrochemical AC impedance (EIS) showed that the lithium ion diffusion coefficient of the LiFe 0.7 Mn 0.25 Mg 0.05 PO 4 /C sample reached 1.19×10 -13 cm 2 /s, which was 4.1 times higher than that of the pre-modified sample. Combined with the cyclic voltammetry (CV) test results, it was found that the appropriate amount of Mg 2+ doping could reduce the impedance and polarization of the material as well as increase the conductivity and lithium ion diffusion rate, ultimately improving the electrochemical properties.

Keywords: lithium-ion battery, LiFe0.7Mn0.3PO4, ion doping, Electrochemical performance